Title: pubkey decompression
Post by: RBan on July 22, 2020, 06:36:10 PM
Anyone know how to modify this code so that it converts the input public key into a compressed P2PKH address instead of uncompressed ? def public_key_to_address(public_key):
#print('Wanting to [%s] this to address'%public_key)
output = []; alphabet = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
var = hashlib.new('ripemd160')
try:
var.update(hashlib.sha256(binascii.unhexlify(public_key.encode())).digest())
var = '00' + var.hexdigest() + hashlib.sha256(hashlib.sha256(binascii.unhexlify(('00' + var.hexdigest()).encode())).digest()).hexdigest()[0:8]
count = [char != '0' for char in var].index(True) // 2
n = int(var, 16)
while n > 0:
n, remainder = divmod(n, 58)
output.append(alphabet[remainder])
for i in range(count): output.append(alphabet[0])
return ''.join(output[::-1])
except:
# Nothing
return -1
Title: pubkey decompression
Post by: TheArchaeologist on July 23, 2020, 08:56:56 AM
Anyone know how to modify this code so that it converts the input public key into a compressed P2PKH address instead of uncompressed ?
You don't need to change any code in that function. You pass a compressed public key as parameter to the function and you get the P2PKH-address for the compressed key. Or you pass an uncompressed public key and get the P2PKH-address returned for the uncompressed address. There is no difference between the two in the steps from public key to the base-58 encoded address. #example for uncompressed
pubkey = '041A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E'
print(public_key_to_address(pubkey))
Results in:
Wanting to [041A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E] this to address
1BoatSLRHtKNngkdXEeobR76b53LETtpyT
#example for compressed
pubkey = '021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7'
print(public_key_to_address(pubkey))
Results in:
Wanting to [021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7] this to address
1AYNNMBpXwV7kVveDmFALhCU8VTA3yTs88
Title: Re: pubkey decompression
Post by: HCP on July 30, 2020, 12:20:01 AM
If you're just trying to convert ONE uncompressed pubkey to compressed (or vice versa)... you can use this: https://iancoleman.io/bitcoin-key-compression/ If you want to do it in code, then the algorithm is: 1. Starting with uncompressed Pubkey, drop the "04" prefix
041A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E
--> 1A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E
2. Split into X (1st 32 bytes) and Y (2nd 32 bytes)
1A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E
X -> 1A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7
Y -> ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E
3. Determine if Y is "Even" or "Odd"
If Y = even, then compressed prefix = 02
If Y = odd, then compressed prefix = 03
ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E is an "Even" number, so Compressed Prefix = 02
4. "Compressed" Public Key = Compressed Prefix + X
Compressed Prefix == 02
X == 1A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7
Compressed Pubkey -> 021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7
Title: Re: pubkey decompression
Post by: DougM on July 30, 2020, 06:56:54 PM
If you're just trying to convert ONE uncompressed pubkey to compressed (or vice versa)... you can use this: https://iancoleman.io/bitcoin-key-compression/
Good site! thanks HCP. RBan, I am not 100% sure what you are trying to do in the end, but I have a potentially similar thread going that you might want check out: how do I extract the address from the output scriptPubKey for early coinbse tx? (https://bitcointalk.org/index.php?topic=5265034.msg54884299#msg54884299)
Title: Re: pubkey decompression
Post by: HCP on July 30, 2020, 10:13:45 PM
I got bored and started playing around with this... So, here is my pretty crappy 5 minute Python code that will take any form of the PubKey (compressed/uncompressed) and output the address of the compressed public key. NOTE: The hexstring -> int conversion for "y" should be both Python 2.7 and Python 3 "safe"... If you're using Python 3 there is the int.from_bytes() function available, which is a bit tidier. import binascii
import hashlib
import codecs
def public_key_to_address(public_key):
print('Wanting to convert this [%s] to address'%public_key)
output = []; alphabet = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
var = hashlib.new('ripemd160')
if public_key[0:2] == "04":
print("------------------------")
print("Found UNcompressed PubKey, converting")
#break into x and y components
x = public_key[2:66]
y = public_key[66:]
#print('x: ' + x)
#print('y: ' + y)
#convert hex str to int
y = int(codecs.encode(binascii.unhexlify(y),'hex'),16)
#test if y is "odd" or "even" and assign prefix as appropriate
if 1 == (y % 2):
public_key = "03" + x
else:
public_key = "02" + x
print("Compressed PubKey: " + public_key)
print("------------------------")
try:
var.update(hashlib.sha256(binascii.unhexlify(public_key.encode())).digest())
var = '00' + var.hexdigest() + hashlib.sha256(hashlib.sha256(binascii.unhexlify(('00' + var.hexdigest()).encode())).digest()).hexdigest()[0:8]
count = [char != '0' for char in var].index(True) // 2
n = int(var, 16)
while n > 0:
n, remainder = divmod(n, 58)
output.append(alphabet[remainder])
for i in range(count): output.append(alphabet[0])
return ''.join(output[::-1])
except:
# Nothing
return -1
pubkey = '041A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E'
print("CompressedAddress: " + public_key_to_address(pubkey) + "\n\n")
pubkey = '0408FD4E4E01356F3F0052E35FA186E54F736B209C025DFC5686FF98FF9A367A52520FAC06060EC7B3FEAE3F92EB840399B09E7E82AB332060D882ED4D4829D383'
print("CompressedAddress: " + public_key_to_address(pubkey) + "\n\n")
pubkey = '021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7'
print("CompressedAddress: " + public_key_to_address(pubkey) + "\n\n")
hardcorepawn@HardCorePC:~$ vi pubkey_fun.py
hardcorepawn@HardCorePC:~$ python pubkey_fun.py
Wanting to convert this [041A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E] to address
------------------------
Found UNcompressed PubKey, converting
Compressed PubKey: 021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7
------------------------
CompressedAddress: 1AYNNMBpXwV7kVveDmFALhCU8VTA3yTs88
Wanting to convert this [0408FD4E4E01356F3F0052E35FA186E54F736B209C025DFC5686FF98FF9A367A52520FAC06060EC7B3FEAE3F92EB840399B09E7E82AB332060D882ED4D4829D383] to address
------------------------
Found UNcompressed PubKey, converting
Compressed PubKey: 0308FD4E4E01356F3F0052E35FA186E54F736B209C025DFC5686FF98FF9A367A52
------------------------
CompressedAddress: 1NCasbMhu3gUjmN6nNmrX3Kqb2H6bzY6Lw
Wanting to convert this [021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7] to address
CompressedAddress: 1AYNNMBpXwV7kVveDmFALhCU8VTA3yTs88
hardcorepawn@HardCorePC:~$ vi pubkey_fun.py
hardcorepawn@HardCorePC:~$ python pubkey_fun.py
Even Y uncompressed PubKey
Wanting to convert this [041A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E] to address
------------------------
Found UNcompressed PubKey, converting
Compressed PubKey: 021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7
------------------------
CompressedAddress: 1AYNNMBpXwV7kVveDmFALhCU8VTA3yTs88
Odd Y uncompressed PubKey
Wanting to convert this [0408FD4E4E01356F3F0052E35FA186E54F736B209C025DFC5686FF98FF9A367A52520FAC06060EC7B3FEAE3F92EB840399B09E7E82AB332060D882ED4D4829D383] to address
------------------------
Found UNcompressed PubKey, converting
Compressed PubKey: 0308FD4E4E01356F3F0052E35FA186E54F736B209C025DFC5686FF98FF9A367A52
------------------------
CompressedAddress: 1NCasbMhu3gUjmN6nNmrX3Kqb2H6bzY6Lw
Compressed PubKey
Wanting to convert this [021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7] to address
CompressedAddress: 1AYNNMBpXwV7kVveDmFALhCU8VTA3yTs88
hardcorepawn@HardCorePC:~$ cat pubkey_fun.py
import binascii
import hashlib
import codecs
def public_key_to_address(public_key):
print('Wanting to convert this [%s] to address'%public_key)
output = []; alphabet = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
var = hashlib.new('ripemd160')
if public_key[0:2] == "04":
print("------------------------")
print("Found UNcompressed PubKey, converting")
#break into x and y components
x = public_key[2:66]
y = public_key[66:]
#print('x: ' + x)
#print('y: ' + y)
#convert hex str to int
y = int(codecs.encode(binascii.unhexlify(y),'hex'),16)
#test if y is "odd" or "even" and assign prefix as appropriate
if (y % 2) == 1:
public_key = "03" + x
else:
public_key = "02" + x
print("Compressed PubKey: " + public_key)
print("------------------------")
try:
var.update(hashlib.sha256(binascii.unhexlify(public_key.encode())).digest())
var = '00' + var.hexdigest() + hashlib.sha256(hashlib.sha256(binascii.unhexlify(('00' + var.hexdigest()).encode())).digest()).hexdigest()[0:8]
count = [char != '0' for char in var].index(True) // 2
n = int(var, 16)
while n > 0:
n, remainder = divmod(n, 58)
output.append(alphabet[remainder])
for i in range(count): output.append(alphabet[0])
return ''.join(output[::-1])
except:
# Nothing
return -1
pubkey = '041A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E'
print("Even Y uncompressed PubKey:")
print("CompressedAddress: " + public_key_to_address(pubkey) + "\n\n")
pubkey = '0408FD4E4E01356F3F0052E35FA186E54F736B209C025DFC5686FF98FF9A367A52520FAC06060EC7B3FEAE3F92EB840399B09E7E82AB332060D882ED4D4829D383'
print("Odd Y uncompressed PubKey:")
print("CompressedAddress: " + public_key_to_address(pubkey) + "\n\n")
pubkey = '021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7'
print("Compressed PubKey:")
print("CompressedAddress: " + public_key_to_address(pubkey) + "\n\n")
Output should be: Even Y uncompressed PubKey:
Wanting to convert this [041A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7ACCF8E941F95AE80B8F373229B7A3F83144160D8982E648F60C8E5CB968EC72E] to address
------------------------
Found UNcompressed PubKey, converting
Compressed PubKey: 021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7
------------------------
CompressedAddress: 1AYNNMBpXwV7kVveDmFALhCU8VTA3yTs88
Odd Y uncompressed PubKey:
Wanting to convert this [0408FD4E4E01356F3F0052E35FA186E54F736B209C025DFC5686FF98FF9A367A52520FAC06060EC7B3FEAE3F92EB840399B09E7E82AB332060D882ED4D4829D383] to address
------------------------
Found UNcompressed PubKey, converting
Compressed PubKey: 0308FD4E4E01356F3F0052E35FA186E54F736B209C025DFC5686FF98FF9A367A52
------------------------
CompressedAddress: 1NCasbMhu3gUjmN6nNmrX3Kqb2H6bzY6Lw
Compressed PubKey:
Wanting to convert this [021A87E4688D8B9445B5B038CB3B34C186331F1AB4FC0822DCCA44192043EAB3B7] to address
CompressedAddress: 1AYNNMBpXwV7kVveDmFALhCU8VTA3yTs88
Title: Re: pubkey decompression
Post by: DarkDays on August 13, 2020, 07:37:57 PM
Here's a quote from an old thread that you might find useful. Hi,
I'd like to know if there is a formula to calculate the two possible values of Y from X
I use a library that needs them, and I don't really want to modify it
Actually it's very simple. y 2 = x 3+ ax 2 + b so we need to perform square root to recover y from x. And it turns out that sqrt(a) = a (q+1)/4 Now you just have to pick either the positive or negative solution. If the y that you calculated is even, and the first byte of the key is even, then use this value, otherwise, use the negative value which is q-y. EDIT: relevant code I wrote as a patch for bitaddress.org
ec.CurveFp.prototype.decompressPoint = function(yOdd, X) {
if(this.q.mod(BigInteger.valueOf(4)).equals(BigInteger.valueOf(3))) {
// y^2 = x^3 + ax^2 + b, so we need to perform sqrt to recover y
var ySquared = X.multiply(X.square().add(this.a)).add(this.b);
// sqrt(a) = a^((q+1)/4) if q = 3 mod 4
var Y = ySquared.x.modPow(this.q.add(BigInteger.ONE).divide(BigInteger.valueOf(4)), this.q);
if(Y.testBit(0) !== yOdd) {
Y = this.q.subtract(Y);
}
return new ec.PointFp(this, X, this.fromBigInteger(Y));
}
else {
// only implement sqrt for q = 3 mod 4
return null;
}
};
// for now, work with hex strings because they're easier in JS
ec.CurveFp.prototype.decodePointHex = function (s) {
switch (parseInt(s.substr(0, 2), 16)) { // first byte
case 0:
return this.infinity;
case 2:
return this.decompressPoint(false, this.fromBigInteger(new BigInteger(s.substr(2), 16)));
case 3:
return this.decompressPoint(true, this.fromBigInteger(new BigInteger(s.substr(2), 16)));
case 4:
case 6:
case 7:
var len = (s.length - 2) / 2;
var xHex = s.substr(2, len);
var yHex = s.substr(len + 2, len);
return new ec.PointFp(this,
this.fromBigInteger(new BigInteger(xHex, 16)),
this.fromBigInteger(new BigInteger(yHex, 16)));
default: // unsupported
return null;
}
};
Link is at : https://bitcointalk.org/index.php?topic=162805 Similar topics can be found being discussed at these links: https://bitcoin.stackexchange.com/questions/86234/how-to-uncompress-a-public-key https://gist.github.com/afk11/a3f1174f30e1e8d9ed2d I hope these helped.
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